Reverts VM thread cleanup

runtime/tests/vm/dart/spawn_shutdown_test.dart

-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import 'dart:async';
-import 'dart:isolate';
-
-// Spawn an isolate |foo| that will continue trying to spawn isolates even after
-// the timer in |main| completes. This test ensures that the VM can shutdown
-// correctly even while an isolate is attempting to spawn more isolates.
-
-isolate1(sendPort) {
-  var receivePort = new ReceivePort();
-  sendPort.send(receivePort.sendPort);
-  receivePort.listen((msg) {});
-}
-
-void foo(int count) {
-  for (int i = 0; i < count; i++) {
-    var receivePort = new ReceivePort();
-    Isolate.spawn(isolate1, receivePort.sendPort);
-    receivePort.listen((sendPort) {
-      Isolate.spawn(isolate1,sendPort);
-      receivePort.close();
-    });
-  }
-}
-
-void main() {
-  Isolate.spawn(foo, 100);
-  new Timer(const Duration(seconds: 10), () {});
-}